(1) Field of the Invention
The present invention relates to a traffic shaping control device for an ATM (Asynchronous Transfer Mode) communication network, and more particularly, to a traffic shaping control device used in an ATM communication network for keeping the time interval between adjacent ATM cells of each of connections at a prescribed value or more.
(2) Description of the Related Art
FIG. 10 shows the configuration of a conventional traffic shaping control device. As a cell sorting section 200 successively receives a plurality of ATM cells of different connections, that is, ATM cells with different VPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier) values, it distributes the cells to respective different cell memories 210 to 212 according to VPI/VCI values. Each of the cell memories 210 to 212 stores cells distributed thereto and, in response to a read signal supplied from a read timing generating section 220, reads out the cells stored therein and outputs same to a cell flow creating section 230. The read timing generating section 220 has a cell output time interval set for each VPI/VCI value and supplies the read signal to each of the cell memories 210 to 212 at corresponding intervals of time. The cell output time interval is set in accordance with the data transmission rate prescribed by an agreement previously made between a subscriber and the carrier.
The cell flow creating section 230 creates a single cell flow from the cells supplied thereto from the individual cell memories 210 to 212. Specifically, individual cells are carried by a sequence of time slots constituting a single signal and are sent out onto a line.
Thus, restrictions are placed on cells which are transmitted from a subscriber at a rate higher than that prescribed by the agreement.
The conventional device, however, requires cell memories equal in number to the connections, giving rise to a problem that large-scale hardware is needed.
Also, the conventional device is constructed such that every cell is once stored in the cell memory. Accordingly, even those cells which are transmitted in conformity with the subscription agreement are unavoidably delayed at the cell memory, and thus there is a demand for a means of eliminating such a delay of cells.
An object of the present invention is to provide a traffic shaping device for an ATM communication network which permits downscaling of the hardware and can eliminate a delay of cells that is caused by performing a delay process on cells which need not be subjected to the delay process.
To achieve the above object, there is provided a traffic shaping control device used in an ATM communication network for keeping a time interval between adjacent ATM cells of each of connections at a prescribed value or more. The traffic shaping control device for an ATM communication network comprises repetition number affixing means for affixing a repetition number of xe2x80x9c0xe2x80x9d to an input cell, delay-controlled cell detecting means for determining based on a VPI/VCI value of the input cell or a delayed cell whether or not the cell concerned is a first type cell which, inclusive of another cell of an identical connection, is not currently present in a delay loop, delay-passed cell detecting means for determining, based on the VPI/VCI value of the input cell or the delayed cell and the repetition number affixed thereto, whether the cell concerned is a second type cell which has passed through the delay loop with another cell of an identical connection currently present in the delay loop, or a third type cell which has not yet passed through the delay loop but with another cell of an identical connection currently present in the delay loop, and for outputting the third type cell with an initial number of repetitions set as the repetition number affixed thereto, number-of-repetitions monitoring means for receiving the second type cell from the delay-passed cell detecting means, checking the repetition number affixed to the received cell to determine whether or not the cell has passed through the delay loop a number of times corresponding to the initial number of repetitions thereof, and for outputting the cell with the repetition number thereof decremented by xe2x80x9c1xe2x80x9d if the cell has not yet passed through the delay loop a number of times corresponding to the initial number of repetitions thereof, flow rate calculating means for receiving the first type cell from the delay-controlled cell detecting means and a cell which, among second type cells, has passed through the delay loop a number of times corresponding to the initial number of repetitions thereof, from the number-of-repetitions monitoring means, calculating a flow rate of the received cell to determine whether or not a predetermined reference flow rate is exceeded by the calculated flow rate, and for outputting a cell of which the calculated flow rate is higher than the predetermined reference flow rate with the initial number of repetitions set as the repetition number affixed thereto, repetition number deleting means for deleting the repetition number from a cell of which the calculated flow rate is judged to be not exceeding the predetermined reference flow rate by the flow rate calculating means, and delay means for subjecting the third type cell output from the delay-passed cell detecting means, the second type cell which is output from the number-of-repetitions monitoring means and of which the repetition number has been decremented, and the first or second type cell which is output from the flow rate calculating means and of which the repetition number has been decremented, to a delay process for a predetermined time and outputting the delayed cell.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.